Use Case

As a... Node.js engineer
I want... to catch a mistaken change in the BSON deserialize API
So that... we do not introduce unintentional changes

User Experience

• What is the desired/expected outcome for the user once this ticket is implemented?
  • BSON.deserialize on bytes that contain the deprecated undefined type return JS undefined
• If bug: What is the number of impacted customers? How severe is the impact? Is anyone blocked or broken?
  • Not a bug

Dependencies

• None

Risks/Unknowns

• What could go wrong while implementing this change? (e.g., performance, inadvertent behavioral changes in adjacent functionality, existing tech debt, etc)
  • No risk, adding a test to reduce risk
• Is there an opportunity for better cross-driver alignment or testing in this area?
  • Possibly, deprecated types are generally not useful but when a driver is deployed for the purpose of building a product over MongoDB rather than an application the ability to interact with these legacy types is necessary, so some degree of support should be maintained.
• Is there an opportunity to improve existing documentation on this subject?
  • Yes, the deserializer returns undefined and the serializer ignores those values by default. The driver however defaults ignoreUndefined to false, so it mitigates that potential surprise.

Acceptance Criteria

Implementation Requirements

• None

Testing Requirements

• Add a test to assert JS undefined is returned when BSON contains deprecated undefined
• Assert ignoreUndefined=false inserts a BSON null for undefined values
  • Organizational: find existing BSON undefined tests and move them to a file of that name.

Documentation Requirements

• https://www.mongodb.com/docs/drivers/node/current/fundamentals/bson/undefined-values/
  • This page should clarify that undefined is returned from the driver when encountered

Follow Up Requirements

• WRITING-15419